Add test of remove_duplicate_coords; simplify open_cubed_sphere#13

nbren12 merged 4 commits intoai2cm:feature/post-process-timestepsai2cm/fv3net:feature/post-process-timestepsfrom

spencerkclark:re-coarse-grainspencerkclark/fv3net:re-coarse-grainCopy head branch name to clipboard